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The Dead Zone and Mississippi River

Draining 31 U.S. states and parts of Canada, the Mississippi River meanders southward and picks up contaminants like sediment, mercury, fertilizers and pesticides. Pollution from fertilizers, sewage treatment plants, and industrial facilities combines to create a Dead Zone in the Gulf. Since the 1970’s, the Dead Zone has grown to the size of Connecticut (about 5,500 square miles). In the Dead Zone, sea life must swim away or suffocate due to lack of oxygen.

Farm runoff and sewage discharges contain massive amounts of nitrogen and phosphorus. Nitrogen and phosphorus polluted water acts as a fertilizer of algae, resulting in large algal blooms. When the algae die, they sink to the saltier water below and decompose, depleting already low oxygen in the deeper water. Because the cooler Gulf waters do not mix well with the lighter and warmer fresh waters from the Mississippi River, oxygen in the water is not replenished, resulting in a large Dead Zone in bottom waters.

Credit: U.S. EPA

The Mississippi River is truly one of the great natural resources of our country. In addition to providing drinking water for more than eighteen million people, the Mississippi and its tributaries provide an engine for economic development, an important transportation link, abundant recreational opportunities and a vast habitat for wildlife. Forty percent of the nation’s migratory waterfowl fly along the Mississippi River corridor, and the Mississippi supports a whopping 260 fish species.

The Mississippi River, however, is not without problems. As the Mississippi meanders southward, it picks up contaminants, including sediment, mercury and pesticides. In addition, nitrogen and phosphorus pollution from upstream farms using excess fertilizer, urban storm sewers and sewage treatment plants combine to create a Dead Zone in the Gulf. The nitrogen and phosphorus polluted water acts as a fertilizer of algae, resulting in large algal blooms. When the algae die, they sink to the saltier water below and decompose, depleting already low oxygen in the deeper water. Because the salty bottom waters do not mix well with the lighter, fresh water from the Mississippi River, oxygen in the water is not replenished, resulting in a large Dead Zone in bottom waters.

The Dead Zone causes untold costs each year to the $2.8 billion Gulf commercial and recreational fishing industries. Inconsistent implementation of the Clean Water Act impacts any efforts to improve the health of the Mississippi River. While some states have begun to take efforts to reduce nitrogen and phosphorus pollution, others lag far behind.

This massive problem could be addressed if state and federal agencies took the problem seriously. For our part, GRN’s work on the Dead Zone includes:

Pushing states and EPA to establish limits on nitrogen and phosphorus pollution in the Mississippi River Basin.

Holding emitters of nitrogen and phosphorus pollution, such as sewage treatment plants, accountable.

Advocating for the appropriate distribution of farm subsidies. Subsidies should be directed towards farmers that actively reduce the pollution flowing off of their crop land.